power amp vs. preamp breakup characteristics

DrNick

DrNick

Inspired
I was playing with a patch earlier that is pretty clean, but just on the edge of breaking up a bit when I play hard (with high-output active pickups, in my case). I was toying with the drive and master volume to experiment with this breakup and wasn't so clear on what I was hearing. The character is definitely different, but I can't put my finger on it because it's pretty subtly applied in this situation.

So, by way of a general question: in this context of a mostly clean tone just starting to distort, how do you think of the characteristics of the power amp vs. the preamp distorting? Which do you shoot for in this situation?

Thanks for any words of wisdom.
 
Latter would be my thinking, we are blessed that we can run these amps to where the power amp's distorting and be in the same vicinity. :) I know my old MkIII Qualified!

There are a lot of amps that just by rolling off the vol on your gat will clean up nicely but still bite if you dig in though I only have passive pups in my jem. I'd guess that your pups could push most amps into that area wouldn't they?

The Fender twin reverb was surprisingly dirty to me yet I'd always thought of it as a clean amp.




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Power amp distortion is as unique and variable dependent as preamp distortion. Every power amp sounds a little different when you start to push it - especially depending on the nature of the preamp that's feeding it. Sorry to be so vague, but there really isn't a one size fits all.
 
DrNick said:
So, by way of a general question: in this context of a mostly clean tone just starting to distort, how do you think of the characteristics of the power amp vs. the preamp distorting? Which do you shoot for in this situation?

Thanks for any words of wisdom.
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That's like asking, "In the context of making a light chicken soup, which should I use: salt or pepper?" The best soup is made by a cook who uses both, and who tastes the soup as he cooks it.


Here's an oversimplified description of both:

Preamp distortion tends to come on quickly as you raise the level. It's relatively smooth. Too much of it can destroy your dynamics and make your tones sound more or less alike.

Power amp distortion tends to come on more gradually and be more responsive to playing dynamics. It tends to be more raw. Too much of it can make your tone flubby.​


For most tones, you want to be pushing the power amp at least a little bit. More for lower-gain tones, less for higher-gain tones. In general; you really have to play around until you find what "tastes" right.
 
I tend to find that playing the sort of music that uses the vol knob for dynamics is DEFINITELY the sort of thing you play with power amp distortion for. You still have rich, pleasant tones when playing lightly, but it opens up and flares when heavy.

Preamp distortion, to me, is much "gainier" and is much more a yes-or-no situation - red versus blue, to power amp distortion's shades-of-red approach.
 
Power amp distortion in 'real' amps is rather difficult to achieve, and once there, it is highly doubtful one could perceive it due to the coincident Phase Inverter (PI) distortion. To get to power amp distortion, one must run nearly full-tilt, and if you can stand in the same room as a 100W Plexi on full-tilt - I hardly doubt you will notice much nuance. ;) PI distortion will swamp-out almost all of the power amp distortion for most cases, and I'm sure modeling this is part of the 'secret sauce' (as there is a lot going on in a 'real' PI cct.).
 
Phase-Inverter distortion can dominate power tube distortion—or not. It depends on how the power amp parameters are set. For example, play with bias, and you'll hear a difference.

The phase inverter is part of the power amp, and phase-inverter distortion is one component of power amp distortion.
 
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